作为一种慢性、进行性的退行性关节病,创伤性骨关节炎(post-traumatic osteoarthritis,PTOA)主要继发于关节创伤、运动外伤[1-3]。瑞典的一项回顾性研究发现手术会提高PTOA发病率[4]。近年来研究显示[5-6],关节外伤迁延为骨关节炎的风险约为20%,有时甚至超过50%。对于严重关节外伤,多采用关节镜下清理术、重建手术或者关节置换术,但手术并不能降低罹患PTOA的风险[7]。

软骨细胞合成胶原纤维和蛋白多糖等基质成分,是形成和维持软骨的重要细胞。关节软骨在层次上分为浅表区、过渡区、深区及钙化软骨区(图1)。Grogan等[8]发现,软骨细胞生物学功能多样,参与蛋白翻译、受体对话、信号转导等。高强度外力瞬间作用于关节可造成关节软骨严重损伤[9],激活软骨细胞引起局部炎症反应[10],产生多种病理变化[11-13](图2),患者关节反复疼痛,可伴有关节肿胀、僵硬、负重能力下降及活动障碍等表现,严重者可致畸形甚至残疾。PTOA发病机制主要涉及:(1) 创伤后关节部分区域的生物力学改变[14];(2) 软骨细胞介导的炎性介质的释放[10,15]。因此,软骨细胞的活化和损伤是骨关节炎的重要发病机制之一,明确PTOA的发病机制有助于开展PTOA的预防和治疗。

(1) Superficial zone;(2) Transitional zone;(3) Deep zone;(4) Tidemark;(5) Subchondral bone.

图1　关节软骨的基本结构 Fig 1　Basic structure of articular cartilage

力传导通路激活软骨细胞的研究进展　研究表明,软骨细胞的初级纤毛可视为机械性刺激感受器,接受力学刺激信号[16-17]。若初级纤毛缺失,关节软骨则相应增厚且刚度降低,深区和软骨下骨的压缩模量显著减小[18]。创伤后关节物理形态改变造成软骨细胞表面的初级纤毛弯曲或拉伸[19],激活了软骨细胞膜表面的受体[20],例如整合素、G蛋白、离子通道等通过信号转导,参与调控PTOA的病程进展[21]。软骨细胞介导骨关节炎信号通路的最新研究进展主要如下(图3)。

(1) Swelling joint;(2) Damaged surface;(3) Infiltration;(4) Osteophyte;(5) Thickening and stiffening of subchondral bone.

图2　创伤后关节软骨的病理变化 Fig 2　Pathological changes of articular cartilage after injury

焊接空心球节点和螺栓球节点各有优劣，总体而言，焊接球节点适应性好，承载力高，而螺栓球节点现场焊接工作量少，施工速度快。柔性直流换流站中通常有高、低端阀厅共4座，若全采用焊接空心球节点，则焊接安装工作量非常大，相比之下螺栓球节点在缩短工期方面具有明显优势。为节约工期，本工程网架节点优先采用螺栓球节点，仅当个别部位杆件内力过大或螺栓球构造不满足要求时，才采用焊接空心球节点。

Ca2+信号相关通路　Ca2+信号参与多种信号转导通路,例如G蛋白耦联受体、电压门控Ca2+通道等。软骨细胞力传导通路也聚焦于Ca2+信号通路[22]。软骨细胞初级纤毛接受力传导信号后,鞭毛内运输蛋白由质膜向胞内传递信号[23],而蛋白装卸与运输离不开Ca2+依赖的激酶活化[24]。整合素(integrin)、嘌呤受体2 (purine receptor 2,P2)、瞬时受体电位蛋白V4型(transient receptor potential vanilloid 4,TRPV4)和Piezo受体参与活化Ca2+信号。

P2可介导应变诱发的新式信号转导通路[31]。研究证实,软骨细胞P2X受体和P2Y受体与经Connexin43通道外流的ATP结合后,介导胞内Ca2+信号调节激酶ERK1/2的磷酸化过程[32],转活转录辅助因子CITED2与转录因子Sp1和HIF1α结合后,促使软骨细胞下调基质金属蛋白酶(matrix metalloproteinase,MMP)家族中MMP1/13的表达。但是该通路在轻度周期性单轴应变(5%,1 Hz)才能起作用。在较强应变条件下P2通路如何调控软骨细胞MMPs表达尚未见报道。

力传导通路改变软骨细胞生物学功能　创伤作用于软骨可直接导致软骨细胞死亡[48],或者通过Fas/FasL[49]、一氧化氮[9]、核酸表达[50-51]等途径间接诱导软骨细胞凋亡,并促进软骨细胞分泌基质分解酶。创伤后软骨细胞大量分泌此类酶,加速恶化软骨原有力学结构,从而导致更严重的力学失衡,加重软骨基质损毁。

整合素是连接基质和细胞蛋白骨架的跨膜受体,创伤后胶原纤维、黏附分子、纤连蛋白等胞外片段与整合素结合,诱发整合素构象改变,进而活化胞内的黏附斑激酶FAK,激活下游Ca2+依赖的蛋白激酶,从而介导胞外信号向胞内转导[25]。Garciadiego-cazares等[26]在大鼠PTOA模型中发现,PTOA早期整合素α1、α5亚单位有较高表达,推测可能与软骨细胞增殖和软骨基质的维持有关,并可对抗PTOA早期病变[27];而在PTOA中后期αV亚单位有较高表达,并且此时软骨组织中α5亚单位表达量显著降低,这提示αV亚单位可能介导PTOA发病过程中软骨细胞的肥大和功能亢进。但是,也有研究指出α5亚单位促进了骨关节炎的典型病变[28-29]。以上研究均说明PTOA中存在异常力传导信号,通过整合素通路调控软骨细胞功能[30]。

图3　创伤导致的力学改变对软骨细胞力传导通路的影响 Fig 3　Influences of mechanical alterations induced by injury on the chondrocyte mechanotransduction

软骨基质分解酶类　带有血小板凝血酶敏感蛋白样模体的解聚素和蛋白金属蛋白酶(a disintegrin and metalloproteinase with thrombospondin-like motifs,ADAMTS-4/5)是降解软骨基质蛋白聚糖的主要酶类。TNF-α和IL-1可促进软骨细胞ADAMTS-4的表达量上调[55],这可能是由其基因启动子中的特异性CpG岛去甲基化介导的[56]。ADAMTS-5的表达不仅受前述多种信号通路的调控[21,39],多种miRNA也具有调控ADAMTS-5基因表达的作用,例如miR-148a[57]、miR-15a[58]、miR-105[59]具有下调作用。

TRPV4为一种Ca2+通道,在软骨细胞初级纤毛和质膜上均有表达[33]。正常状态下,TRPV4介导的Ca2+信号通路对维持基质和关节稳态有重要作用,TRPV4介导的软骨基质低渗透压信号通过升高胞质内的Ca2+浓度调控细胞基因表达[34-35]。TRPV4突变或功能被抑制时,则影响基质的合成及关节的力学特性[35],致使关节退变。O’conor等[35]提出利用TRPV4激动剂GSK1016790A增强基质合成,从而治疗PTOA的思路。

Hedgehog信号通路　Hedgehog信号通路在骨关节炎发病中也起到重要作用。碎片蛋白1(patched homologue 1,Ptch1)受体与基质蛋白成分结合后,活化初级纤毛上的润滑蛋白(smoothened,Smo),从而促进Gli家族蛋白活化并入核作用于Wnt和Ptc基因。Thompson等[21]研究发现,10%周期性张应变作用于牛软骨细胞后,通过该通路促进软骨基质中蛋白多糖酶ADAMTS-5的表达,加速基质退变。

经典Wnt信号通路　经典Wnt信号通路以卷曲蛋白Frizzled和低密度脂蛋白LRP5/6为主要复合受体,当配体Wnt蛋白与受体结合后,胞内β-连环蛋白(β-catenin)含量升高,与核内转录因子T细胞因子/淋巴增强因子(TCF/LEF)结合后,启动靶基因转录,从而促进软骨细胞的增殖[37]、Ⅱ型胶原的分泌[38]。然而,Wnt通路与骨关节炎的发生具有争议。Yuasa等[39]指出该通路促进兔软骨细胞MMP-3/13以及ADAMTS-5表达,损伤关节软骨;而Nalesso等[40]和Ma等[41]研究发现人软骨细胞β-连环蛋白与NF-κB相互作用可抑制MMP1/3/13表达,保护软骨。

党校作为锻造党员干部的主阵地和大熔炉，在实施生态文明建设这一国家战略中，要充分发挥自身独特优势，积极作为，为生态文明建设培养“三型”党员干部。

Piezo1和Piezo2受体是软骨细胞膜上的跨膜蛋白,属于机械门控性Ca2+通道。Lee等[36]发现其在猪原代软骨细胞上有丰富表达,同时证实Piezo1和Piezo2受体参与维持Ca2+内流。高应变力信号破坏软骨稳态,利用GsMTx4阻断Piezo1/2通道或特异性小干扰RNA迫使Piezo1/2通道失活,均可抑制创伤后软骨组织中软骨细胞死亡,由此提出降低Piezo1/2介导的关节损伤性力传导信号来治疗PTOA的新思路。

TGF-β/BMP信号通路　转化生长因子(transforming growth factor,TGF)超家族中的TGF-β和骨形成蛋白(bone morphogenetic protein,BMP)等配体与细胞膜受体胞外区结合后,使胞内信号蛋白Smads磷酸化,转移到细胞核内与特异性靶基因序列结合,或与DNA结合蛋白相互作用调控靶基因的表达[42]。研究证实,PTOA患者关节中TGF-β水平过低或者过高均诱导软骨丧失正常力学特性和功能,促进MMPs过表达[43-44],引起软骨退变、基质降解、骨赘形成等PTOA特征性改变[45-46]。

上述4种信号通路虽是独立的,但也存在相互作用。在PTOA发病中,软骨细胞中整合素除与Ca2+通路相关,还与TGF-β/BMP信号通路中的GDF-5和BMP-7等相关,BMP-7的上调可增加整合素αV亚单位表达,这与中后期PTOA的发病相关,而GDF-5与α5亚单位表达相关,PTOA中可能被抑制。而在另一研究中,Wnt信号通路诱导的WISP1蛋白作用于TGF-β信号通路可能促进骨关节炎中典型病变的发生[47]。多种信号通路相互作用说明力传导信号介导PTOA发病机制的复杂性。

在下属混凝土公司关停过程中，改制工作小组从“零经验”开始，在学中干、干中学，深入学习《公司法》《劳动法》等法律法规，以及国有企业改制方面的政策，党组织站在工作第一线，充分发挥党的政治优势、组织优势和密切联系群众的优势，深入做好解疑释惑和思想疏导工作，引导职工转变择业观念，帮助他们搭建再就业平台，解决后顾之忧，迅速圆满完成关停改制。

1.由州局兽医科和州动物卫生监督所抽调执法人员组成专项整治小组，各县市畜牧兽医局对辖区内的产地检疫申报点、生猪规模养殖场、散养户、牲畜交易市场、生猪定点屠宰厂进行监督检查。

非免疫系统细胞(软骨细胞、成纤维细胞及滑膜细胞等)分泌促炎因子[52]进一步加强软骨细胞的凋亡[51],破坏基质,加重软骨力学负荷的失衡,甚至导致软骨发生损毁而直接暴露软骨下骨[1]。大量研究表明PTOA中存在抗炎因子[53-54]。

MMPs降解胶原的蛋白成分促进关节损伤。骨关节炎患者关节中的MMPs活性比正常关节显著增高,不仅降解已有胶原纤维,还会抑制新生基质形成,造成创伤所致的损伤难以愈合。中后期骨关节炎软骨细胞中MMP3/9/13基因启动子的CpG岛去甲基化,有助于相关蛋白酶量的增加[60-61]。与ADAMTS-5相似,MMPs的表达也受到miRNA的调控,例如miR-127-5p[62]、miR-148a[57]、miR-320[63]下调MMP-13的表达;miR-140[64]、miR- 411[65]却上调MMP-13的表达。近年来,类似miRNA不断被发现,miRNA正成为PTOA的研究热点。Saito等[66]给予人软骨细胞单轴周期性拉应变(10%,0.5 Hz),发现组蛋白去乙酰化酶的拮抗剂可抑制MMP3/13的表达。

促炎因子与抗炎因子　损伤相关分子模式(damage-associated molecular pattern,DAMP)是组织或细胞受到损伤、缺氧、应激等因素刺激后释放到细胞外的一类物质。软骨在创伤损伤后,通过模式识别受体(pattern recognition receptor,PRR)识别的DAMP,包括透明质酸[67]、核酸片段、ATP等。透明质酸、核酸片段通过Toll样受体活化转录因子NF-κB增强促炎因子TNF-α、IL-1β和IL-6的表达。研究显示,在小鼠膝关节关节面骨折后急性期反应,关节内主要是IL-1β起促炎作用[68]。另外,滑膜液和软骨内存在大量的TNF-α、IL-1β和IL-6等因子[69],同时基质分解酶类的表达增加[44,64,70]。提示DAMP与PRR相互作用,通过炎症加快基质降解,促进软骨细胞的凋亡,加剧PTOA病变。

三是，2017年4月26日—4月27日，由埃里斯塔车行至阿斯特拉罕，重点访察沿途的查干阿姆、伏尔加河渡口、和硕特庙和阿斯特拉罕的小克里姆林宫——沙俄时期阿斯特拉罕将军衙门所在地；

对比手术指标以及并发生症发生情况：对患者的手术各项指标进行统计分析，手术治疗效果通过患者手术时间、术中出血量以及住院时间来分析。计算患者护理期间出现并发症的例数以及并发症总发生率[9-11]。

机体为维持关节稳态,需要保证炎症与抗炎反应的动态平衡。抗炎因子在PTOA中也扮演重要角色,包括IL-1受体拮抗剂(IL-1 receptor antagonist,IL-1Ra)、IL-4、IL-10、IL-13、TGF-β1等[71-73]。Zhang等[54]在成年兔中转染IL-1Ra和TGF-β1,发现单一抗炎因子就能促进损伤软骨的修复,两因子共表达则有协同效应。Agarwal等[74]研发的纳米级IL-1Ra-poly-pyridine颗粒通过阻断NF-κB途径抑制IL-1β合成,进而抑制炎症。另外,IL-10能促进软骨细胞合成蛋白多糖[72],有研究提示锻炼也可促进滑膜内和软骨中IL-10的合成[75-76]。

结语　由于关节软骨内并不存在免疫细胞,因此转变为成纤维细胞样的软骨细胞可视为软骨细胞生物学和分子生物学应答的中心,其中力学因素和炎症因素的协同作用,对PTOA的发病和进展有重要效应。然而,对关节软骨不同区域内软骨细胞的力学信号通路和炎症反应通路的机制研究还很有限。这些通路中分子作用的靶点将是预防、治疗PTOA和良好预后的研究方向。

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